The present invention is for a vibration attenuator for use with a disk brake lathe to reduce noise and vibrations resulting from machining the surfaces of a brake disk by the lathe.
Automotive brake disks are periodically resurfaced by a disk brake lathe in order to maintain adequate operation. The disk brake lathe typically has a pair of cutting tools, each attached to a tool holder by a fastener to allow replacement when the cutting tool becomes worn. The tool holders position the cutting tools against the surfaces of the brake disk to establish a desired depth of cut, and then maintain the cutting tools in position as they are drawn across the disk surfaces while the lathe rotates the brake disk in order to machine the disk surfaces. Typically, the desired depth of cut is set at a position near the center of a radius of the disk surface while the brake disk is rotated, and the cutting tools are then moved toward the center of the brake disk to begin the machining process. The cutting tools are then moved radially outwards to resurface the brake disk.
Vibrations caused by the cutting action of the cutting tools on the disk surfaces need to be attenuated, both to reduce chattering of the cutting tools to assure that the resulting machined disk surfaces are sufficiently planar for proper operation, and to reduce undesirable noise in the machining environment. One approach to reducing vibrations has been the use of friction pads which are biased against the disk surfaces and engage the cutting tools, the tool holders, and/or the fasteners.
U.S. Pat. No. 3,710,661 teaches a vibration dampener where friction pads engage either the tool holders or the cutting tools. The friction pads are positioned and biased against the disk surfaces by a scissors-shaped spring, which in turn is pivotably mounted to a cutting head assembly of the lathe. Since the friction pads and spring are mounted to the cutting head assembly on which the tool holders are also mounted, the friction pads move with the tool holders as the cutting head assembly is moved to position the cutting tools near the center of the brake disk and to subsequently advance the cutting tools radially across the disk surfaces. The pivotable mounting allows the spring and friction pads to be pivoted away from the cutting tools to allow the cutting tools to be replaced. Having the vibration dampener attached to the cutting head assembly may make it difficult to position the friction over the disk surfaces. Furthermore, having the spring pivotably mounted can create interference problems if the vibration dampener is to be used on a lathe, such as those made by Pro-Cut International, the assignee of the present application, which has a lock knob mounted to the top of the cutting head assembly. The lock knob serves to secure the tool holders in position once the depth of cut has been set, and typically is too large to allow a spring such as employed in the ""661 vibration dampener to be pivoted past the lock knob.
U.S. Pat. No. 4,531,434 teaches a vibration attenuator which does not require that the spring be mounted to the cutting head assembly. In the ""434 attenuator, friction pads are provided with pins which engage either the cutting tools or the tool holders as the cutting tools are moved radially outwards, this engagement serving to move the friction pads along with the cutting tools as the brake disk is resurfaced. The friction pads are mounted on a U-shaped spring assembly which is independent of the cutting head assembly. However, it has been found that the particular geometry constraints of the ""434 vibration attenuator limit its effectiveness for many lathe configurations. Furthermore, the use of pins extending from the pads may limit usefulness when the clearance above the cutting tools is restricted by a brake caliper bracket associated with the brake disk.
To overcome the limitations of the ""434 vibration attenuator, U.S. Pat. No. 6,227,085 teaches a vibration attenuator where the friction pads are provided with protruding engagement nubs which engage raised heads of the fasteners used to affix the cutting tools to the tool holders when the cutting tools are moved radially outwards. In addition to serving to move the friction pads along with the cutting tools as the brake disk is resurfaced, this engagement is purported to provide superior reduction of vibrations. The ""085 patent reports that the particular geometry of the vibration attenuator is well suited for use with disk brake lathes sold by Pro-Cut.
A limitation of both the ""434 and ""085 vibration attenuators is that they only move the friction pads along with the cutting tools when the cutting tools are moved radially outwards. When the cutting tools are moved radially inwards, the pins become disengaged from the cutting tools or tool holders in the case of the ""434 vibration attenuator, or the engagement nubs become disengaged from the raised head of the fasteners in the case of the ""085 vibration attenuator. In either case, when the cutting tools are moved radially inwards, the friction pads of the vibration attenuator become disengaged and do not move with the tool holders, requiring the vibration attenuator to be repositioned. This requirement is inconvenient in situations where the cutting tools are advanced more than once across the disk surfaces. This can occur if the first pass of the cutting tools over the disk surfaces is found insufficient to provide planar disk surfaces, or if one of the disk surfaces is deeply scored by wear. In such cases, after the cutting tools have been advanced radially outwards, they are moved radially inwards and set with an increased depth of cut, then advanced again across the disk surfaces. The unidirectional limitation of the ""434 and ""085 vibration attenuators requires that the vibration attenuator be repositioned after the cutting tools are moved radially inwards, adding an additional step to the procedure.
U.S. Publication US 2001/0011490 is a continuation-in-part of the application which issued as the ""085 patent, and teaches a nub configuration which is designed for a disk brake lathe sold by Pro-Cut. The nub is configured to affirmatively hold the nub in contact with the raised head of the fastener of the cutting tool as the tool is advanced across the disk surface. The nub also contacts an angled surface on the tool holder, which is reported to move the nub into engagement with the raised head when the disk is rotated. The operation of the ""490 vibration attenuator is dependent on a particular configuration of the tool holders of the disk brake lathe, and thus a particular vibration attenuator would appear to be dedicated to a particular model of lathe.
Thus, there is a need for a vibration attenuator for disk brake lathes which overcomes the deficiencies of the above referenced devices.
The present invention is for an improved vibration attenuator for a disk brake lathe. The attenuator provides a more flexible coupling mechanism for assuring that the attenuator tracks cutting tools of the lathe in a manner appropriate to reduce the vibration of the cutting tools as they traverse disk surfaces of a brake disk. Furthermore, the tracking is bi-directional and allows the attenuator to be positioned by the action of the cutting tools without requiring that the attenuator be affixed to a cutting head assembly used for advancing the cutting tools. Similarly, the design of the attenuator is such that its advancement with the cutting tools is not dependant on the details of the geometry of the cutting head assembly, its tool holders, or the associated cutting tools.
The vibration attenuator of the present invention is designed for use with a disk brake lathe having a cutting head assembly which has a pair of cutting tools. Each of the cutting tools is mounted to an associated tool holder and attached thereto by a fastener. The fastener has a fastener raised head having a head sidewall and a head top. The lathe is provided with means for moving the cutting head assembly such that the tool holders traverse a path that is substantially radial with respect to the brake disk.
The attenuator has a pair of friction pads, each having a disk-engaging surface which, when in service, is brought into frictional contact with a disk surface of the brake disk. Each of the pads is bounded by a pad lower surface which resides between a pad proximal surface and a pad distal surface. Each of the pads contains a pad recess in the pad lower surface. The pad recess is bounded, in part, by a recess distal wall and a recess proximal wall. These recess walls initiate at the pad lower surface and terminate at a recess bottom which is spaced apart from the pad lower surface by a recess depth D, and the recess distal wall and the recess proximal wall are separated by a recess width W of sufficient size to accommodate one of the fastener raised heads. The depth D should be sufficient to assure extended contact between the recess walls and the head sidewall of the raised head, but not necessarily the head top of the raised head. In some embodiments, the recess could extend completely through the pad, but such would limit the useful life of the resulting vibration attenuator as the pads wear.
When the pad recess is placed over the fastener raised head, the fastener raised head engages the recess proximal wall when the cutting head assembly is moved to advance the cutting tools radially outwards across the disk surfaces. This engagement serves to move the friction pad along with the cutting tool and the tool holder associated with the fastener, as well as serving to couple the friction pad with the cutting tool to dampen vibrations. Similarly, when the cutting head assembly is moved radially inwards, the fastener raised head engages the recess distal wall to move the friction pad along with the cutting tool and the tool holder.
It is preferred that a setback X of the recess distal wall from the pad distal surface be provided that is sufficiently large as to maintain each of the pads in contact with its associated one of the disk surfaces when the cutting tools have reached the periphery of the disk. Preferably, the setback X should also be maintained small enough to avoid interference of the pads with a wheel hub associated with the brake disk as the cutting tools approach the wheel hub.
Spring means for forcibly engaging the disk-engaging surfaces of the friction pads with the disk surfaces are provided. One preferred embodiment of the spring means is to employ a U-shaped member having a pair of legs, with each of the legs mounting into the pad proximal surface of one of the pads, and having a tension spring extending between the legs.